Paclitaxel, an alkaloid compound originally derived from the bark of the Pacific yew tree, is currently used in treatment of breast and ovarian as well as many other types of cancer, including non-small cell lung carcinoma, prostate, head and neck cancer, and lymphoma.(1-9) The main site of paclitaxel's action is the microtubules of eukaryotic cells, whose functions include formation of the mitotic spindle during cytokinesis, intracellular transport, shape maintenance, cell motility and attachment, and regulation of transmembrane signals from cell-surface receptors.(10) Paclitaxel acts predominantly by promoting the polymerization of tubulin subunits into microtubules and by preventing depolymerization of the microtubules once they are formed.(11) Paclitaxel has been shown to block cell growth in the G2-M phase of the cell cycle, with subsequent inhibition of mitosis.(12,13) Changes in the structure of microtubules and the mitotic spindle apparatus lead not only to inhibition of cellular division and migration of chromosomes but also to chromosomal breakage.(14)
Sphingomyelin, a cell membrane component, can be hydrolyzed to ceramide and phosphorylcholine by acid or neutral sphingomyelinase.(15,16) This hydrolysis event initiates an intracellular signalling cascade associated with the stimulation of numerous biological activities, including induction of apoptosis(17-24) and arrest of cell growth in the G0-G1 phase.(25-27)
The rationale for combination of paclitaxel and ceramide is based on previous studies that demonstrated activation of Fas expression on leukemic cells by another chemotherapeutic agent, vincristine, which acts primarily by destroying the mitotic spindle in the G2-M phase.(28-30) Since ceramide has been reported to mediate, in part, Fas activation,(15,22,23) two agents that appear to converge on some common point in the sphingomyelin/ceramide pathway was evaluated.
Moreover, since these agents act in different phases of the cell cycle, and not all tumor cells can be arrested and/or eliminated in the G2-M phase by paclitaxel exposure, additional anti-cancer agents may be needed in the therapeutic regimen. This is supported by the observation that paclitaxel combined with other chemotherapeutic agents in treatment of a variety of cancers, including leukemia, typically produces a stronger tumor cell growth inhibition than a single chemotherapeutic agent.(31-33) Therefore the experiments combine ceramide, a reported G0-G1 blocker, with paclitaxel to prevent proliferation of cells that escape the G2-M arrest induced by paclitaxel.
This invention provides a method of combination therapy wherein paclitaxel (or other chemotherapeutic agents) and ceramide interact synergistically to induce cytotoxicity and apoptosis in carcinoma cells thereby decreasing the growth of cancer cells.